Teasing Darkseid already.
I didn't have a problem with Steppenwolf as the main villain, as long as they hinted at who he was working for (even though that would have been copying again from the first Avengers film, Loki working for Thanos) but getting mentioned once by Steppenwolf wasn't good enough. A short cameo shot would suffice for me.
But if they want me to respect Darkseid like I do Thanos, having him NOT get solo'd by Superman is the minimal requirement.